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Patients with renal disease who present early in the course of illness
typically have abnormalities of urine volume or composition (eg,
presence of red blood cells or abnormal amounts of protein). Later,
they manifest systemic symptoms and signs of lost renal function
(eg, edema, fluid overload, electrolyte abnormalities, and anemia).
Depending on the nature of the renal disease, they may progress—rapidly
or slowly—to display a wide range of chronic complications
resulting from inadequate residual renal function.

Because there are no pain receptors within the substance of the
kidney, pain is a prominent presenting complaint only in those renal
diseases (eg, nephrolithiasis) in which there is involvement of
the ureter or the renal capsule.

Because of the crucial role of the kidney in filtering blood,
a wide range of systemic diseases and disease of other organ systems
may be manifested most prominently in the kidney. Thus, renal disease
is a prominent presentation of long-standing diabetes mellitus,
hypertension, and autoimmune disorders such as systemic lupus erythematosus.

Without treatment, renal disease may result in sufficient loss
of kidney function to be incompatible with life. However, not all
renal disease has an inexorable downhill course and dismal outcome.
The consequences of renal disease depend on the extent and nature
of the injury and its natural history and time course. Some forms
of renal disease are transient. Even when severe, they may be self-limited
and reversible and, if managed properly, may have no permanent consequences.
Other forms progress eventually to renal failure, either rapidly
or slowly, with associated metabolic and hemodynamic consequences.
When renal disease progresses, there can be loss of renal filtration
capacity (eg, disordered regulation of body electrolyte and volume
status) as well as loss of nonexcretory renal functions such as
the production of erythropoietin, resulting in anemia.

Checkpoint

Anatomy, Histology,
& Cell Biology

The kidneys are a pair of encapsulated organs located in the retroperitoneal
area (Figure 16–1). A renal artery
enters and a renal vein exits from each kidney at the hilum. Approximately 25% of
cardiac output goes to the kidneys. Blood is filtered in the kidneys,
removing wastes—in particular urea and nitrogen-containing
compounds—and regulating extracellular electrolytes and
intravascular volume. Because renal blood flow is from cortex to
medulla and because the medulla has a relatively low blood flow
for a high rate of metabolic activity, the normal oxygen tension
in the medulla is lower than in other parts of the kidney. This
makes the medulla particularly susceptible to ischemic injury.